Which sample type is submitted for testing by a private individual or firm?

The appropriate choice in this context is the service sample. A service sample is designated for use by private individuals or firms seeking to have their seeds tested for various reasons, such as quality control or compliance with market standards. This type of sample is typically submitted voluntarily, allowing the submitter to obtain analysis results that can inform them about the condition or viability of their seed lots.

In contrast, certification samples are specifically associated with the seed certification program and are collected to verify that seeds meet certain standards for purity and quality before being sold or planted. Official samples are taken by authorized inspectors during regulatory inspections or compliance checks, and they hold legal significance. Miscellaneous samples do not correspond to a specific purpose as clearly as service samples and are often used in irregular circumstances or for purposes not covered by the other categories. Thus, the role and intent behind a service sample align perfectly with submissions from private individuals or firms.